Muscle weakness is when your muscles can’t function at their usual capacity. This is common and is usually not a concern. Depending on the cause, muscle weakness might affect your shoulders, legs, face, arms, hips, or other body parts.
Everyday causes of muscle weakness include:
- excessive movement, such as exercise, walking long distances, or physical labor
- fatigue or a lack of sleep
- a recent viral or bacterial infection that’s left you feeling weak
In other cases, muscle weakness may signal a health condition, such as multiple sclerosis (MS), chronic fatigue syndrome (CFS), or a hormone imbalance.
If you’re concerned about new, sudden, or persistent muscle weakness, consider talking with a doctor. They can assess your symptoms and suggest the most appropriate treatments or remedies.
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1. Excessive movement
The first cause a healthcare professional will rule out is muscle fatigue.
You might have noticeably weaker muscles after starting a new exercise regime or returning to exercise after spending time sedentary, such as when recovering from an illness.
Healthcare professionals will also rule out whether you’re experiencing pain-related movement problems with usual muscle strength, rather than true muscle weakness.
If they rule out these factors, they may test your muscle strength using an objective tool called the Medical Research Council Muscle Scale. Depending on the results, they may recommend further diagnostic tests.
2. Age-related muscle weakness
Everyone begins to lose muscle mass and strength as they get older, potentially starting as early as age 30 years. This is a typical bodily process.
Muscle strength reduces more quickly in some people, which is known as sarcopenia. This affects an estimated 10% to 16% of older adults.
Symptoms of sarcopenia include:
- muscle weakness
- falling
- walking slowly
- perceived muscle wasting
- having difficulty doing usual daily tasks
Getting more exercise, especially strength training, and following a protein-rich diet may help with these symptoms.
3. Vitamin and mineral deficiencies
Some vitamin deficiencies and mineral deficiencies can cause muscle weakness.
For example, a 2018 case study reports that vitamin D deficiency can lead to proximal muscle weakness, which means weakness near the center of the body, and an increased risk of falls.
Other nutrient deficiencies linked with muscle weakness include:
- calcium deficiency (hypocalcemia)
- potassium deficiency (hypokalemia)
- vitamin B12 deficiency
If you suspect a vitamin or mineral deficiency, consider asking a doctor for blood tests. Taking vitamin supplements is a common and effective treatment option.
4. Chronic fatigue syndrome (CFS)
People with CFS — also known as myalgic encephalomyelitis (ME) or ME/CFS — experience extreme fatigue after small amounts of activity.
The Centers for Disease Control and Prevention (CDC) report that up to 3.3 million people in America may have CFS.
This fatigue may feel like muscle weakness, though the muscles themselves haven’t lost strength. People with CFS may have difficulty maintaining muscle tone as they aren’t able to do as much physical activity.
Other symptoms of CFS include:
- difficulty sleeping
- problems with thinking and memory
- symptoms worsening when standing or sitting up
- pain, such as muscle aches, headaches, or joint pain
- a sore throat
- digestive issues, including irritable bowel syndrome
There’s no specific treatment for CFS, but over-the-counter painkillers, healthy sleep habits or sleep medication, and mental health treatments may help.
5. Multiple sclerosis (MS)
MS is an autoimmune condition where your body attacks healthy nerve fibers. Nearly 1 million people in the United States live with MS.
Muscle weakness is a common symptom of MS. This may be because you’re moving around less due to pain and fatigue, which means your muscles lose strength. It could also result from damage to the nerve fibers in the spinal cord or brain.
You may feel muscle weakness all over your body or specific body parts, including the arms, hands, legs, feet, facial muscles, and muscles that help you talk or swallow. It can also affect bladder control.
Other symptoms of MS include:
- tingling
- numbness
- memory problems
- mood changes
- fatigue
- pain
Treatment for MS aims to slow the disease course and prevent symptom relapse. A doctor may prescribe medications and rehabilitation methods.
6. Hormonal causes
Various hormonal conditions can cause muscle weakness, including:
Diabetes is another hormonal condition that can affect your muscles. Diabetic neuropathy may affect the nerves that control movement, leading to muscle weakness. If you have diabetes, taking diabetes medication can help with symptoms and complications.
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Get free card7. Neurological conditions
Conditions that affect your brain or nerves — known as neurological conditions — can also affect your muscle strength.
Muscle weakness on one side of the body is more common in brain-related conditions, such as a stroke.
Muscle weakness with pain is more common in nerve-related conditions (neuropathy), such as a pinched nerve. For example, a pinched nerve in your spine can cause muscle weakness in your legs, and carpal tunnel syndrome can cause weakness in your hands.
Rare neurologic causes of muscle weakness include:
- amyotrophic lateral sclerosis (ALS), a rare progressive disease that damages your nerves
- Guillian-Barré syndrome (GBS), a rare condition where your immune system attacks your nerves
- motor neuropathy, a condition that develops in adulthood and causes asymmetric muscle weakness, typically in the upper limbs
- myasthenia gravis, a neuromuscular disorder that causes muscle weakness across the body, including the eyes, throat, arms, and legs
8. Alcohol and other substances
Excessive alcohol use can lead to muscle weakness. Alcohol is toxic to the nerves and muscles.
Other recreational substances can also lead to muscle weakness, including:
- cocaine
- amphetamines
- opioids
Treatment for substance use disorders can include detox programs, medications, and therapies.
9. Medication side effects
Various medications can cause muscle weakness as a side effect, including:
- cholesterol-lowering drugs, including statins and fibrates
- omeprazole (Prilosec), which treats acid reflux
- fluoroquinolones, a type of antibiotic
- glucocorticoids, a class of steroid
- antiretroviral drugs to treat HIV
- penicillamine, which treats rheumatoid arthritis
- hydroxychloroquine (Plaquenil), an antimalaria drug
- cancer medications, including interferon alfa and hydroxyurea
If you think your medication may be causing muscle weakness or other undesirable symptoms, consider talking with a doctor about adjusting your medications.
10. COVID-19 infection
Early research, including a 2022 review, suggests that mild, moderate, and severe COVID-19 can cause muscle and skeleton symptoms as well as affect your respiratory system.
Many people experience musculoskeletal symptoms for months after having COVID-19. This is known as long COVID. Symptoms of long COVID can include:
- fatigue
- muscle aches
- joint pain
- muscle weakness
The researchers say more research is needed — especially muscle imaging and analysis of muscle tissue — to determine how COVID-19 affects the muscles. Possible causes include inflammation, muscle disease, or another disorder directly or indirectly related to COVID-19.
Summary
Muscle weakness has a vast range of possible causes, including:
- muscle fatigue after exercise
- age-related muscle weakness
- vitamin deficiencies
- hormonal causes
- chronic conditions, like MS and CFS
- neurological conditions
- alcohol use
- a side effect of medications
- long COVID
The most appropriate treatment differs depending on the cause. A healthcare professional may recommend medication, therapies, or lifestyle strategies to help with your symptoms.
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